A number of devices have been developed over the years for detecting and measuring torsional vibrations in the various shaft sections comprising the total shaft of a turbine-generator set. These devices have been employed in testing programs as well as continuously on-line to protect the turbine-generator from damaging torques which accompany such vibrations. It has been found that, in large turbine-generator systems, even very small torsional oscillations in the shafts can cause stresses which may damage the shafts, and in the most extreme cases, result in shaft breakage and destruction of the machine itself. These vibrations, manifested as deviations from a uniform angular velocity, appear in virtually all rotating portions of the turbine-generator, including the generator rotor and its associated rotating magnetic field. Because the turbine-generator set comprises a system of multiple masses (including, for example, the various turbine sections, the generator rotor, shaft couplings and so forth), the different shaft sections must be separately considered as having different effects on the overall system.
To monitor torsional oscillations in the dynamoelectric machine portion of a turbine-generator system and specifically in the rotor thereof the previously available methods and devices have not been entirely adequate. This inadequacy stems largely from inaccessibility of the rotor for physical attachment of toothed wheels, light reflective stripes or other indicia which may be detected to provide the fundamental indication of rotor speed and upon which the prior art devices depend. Thus, there is a need in the art for means to monitor the torsional vibrations of the rotor of a dynamoelectric machine, free of the requirement of having physical contact with the rotating member.
Accordingly, it is an object of the present invention to provide a method and apparatus for monitoring torsional vibrations in the rotor of a dynamoelectric machine which will eliminate the need for physical contact, attachments, or other modifications to the rotating member.
It is a further object of this invention to provide a monitor of torsional vibrations in the rotor of a dynamoelectric machine by using the electrical quantities available at the output terminals of the dynamoelectric machine.